Yemen is in chaos.

For the past two days, Shiite Houthi rebels have laid siege to the presidential palace. Now, reports claim that the rebels have seized the palace; and the status of President Abed Rabbo Mansour Hadi remains unknown. Although the Houthi rebels are not targeting Americans—at least for the time being—U.S. officials are preparing for the possibility of a “non permissive environment,” meaning that the city of Sana’a will have descended into combat-like conditions.

Unfortunately for Americans in Yemen, evacuation isn’t simply a matter of driving to the airport and hopping a flight.

CNN explains:

If an evacuation is ordered, the first option would be to have embassy personnel drive to the commercial airport in Sanaa and fly out, the official said. But in the wake of an embassy car being fired Tuesday, the safety of the roads in the capital is now being constantly evaluated, the official said. If embassy workers did drive to the airport it is likely some sort of air cover would be provided, under the current plan.

Other detailed military planning for various options has been finalized, the official said. Those options would be used if a request for military assistance were made.

If helicopters and V-22 aircraft from the ships are sent to Sanaa, it would be a complex operation that could last for several days to fully evacuate “several hundred Americans” from the embassy, the official cautioned. “Nobody should think this would be easy.”

The Houthi rebels claim that they’re working for a more democratic Yemen, but analysts are skeptical of the group’s claims, and worry that a successful coup could lead to further radicalization.

The Houthis are an offshoot of Shiite Islam that is known as Zaydism, and they have put together a militia that has been fighting the central government on and off for the past decade.

The Houthi leader, Abdulmalik al-Houthi, 33, is considered a saint by his followers. The militia, which is widely believed to be backed by Iran, claims it is willing to work with other groups in Yemen and would like a democracy.

But the majority Sunnis feel threatened by the minority Houthis, whose rise could easily lead to increased sectarian friction in Yemen, the poorest of the 22 Arab countries.

“Yemen could become another Afghanistan — a failed state dominated by warlords and extremists, and with even fewer prospects for the young revolutionaries who just three years ago thought their nightmare had ended,” Middle East analyst Robin Wright wrote in The Wall Street Journal.

Unrest has plagued Yemen since 2004, when now-rebels revolted over perceived discrimination on the part of the majority Sunni government. In September, the rebels began to move out of their traditional strongholds in north Yemen and into new territory.

As of right now, plans are to evacuate only State Department personnel if conditions deteriorate; U.S. officials haven’t yet decided whether or not to extend evacuation orders to other Americans in Yemen.